Certain downhole tools such as perforation tools, cutting torches, cementation tools, tools for linings or anchoring tools are often actuated by firing a pyrotechnic system. Such systems typically comprise an explosive charge or an inflammable solid notably for generating a force or/and heat power intended to carry out the operation
In order to carry out such operations safely, the use of an electrical stranded cable is known for lowering the pyrotechnic system into the well. The electrical cable is connected at the surface to an electric power supply unit capable of delivering sufficient power in order to trigger the firing. When the pyrotechnic system has to be triggered, the electric power is transmitted from the surface through the cable right down to the pyrotechnic system.
Such an intervention device is rather costly. Further it is relatively difficult to apply because of the seal to be achieved at the surface, at the head of the well.
In order to reduce the cost of the operation and to facilitate the making of the seal at the surface, it is known how to lower the charge by means of cables of the “piano string” type, designated by the term of slickline.
Such cables are very resistant mechanically. However, the charge has to be triggered by means of a countdown system associated with an acceleration, pressure, temperature sensor in the lower assembly, which makes its triggering not very accurate.
Additionally the safety of the operators at the surface is not guaranteed, since there exists no means for checking that the charge has actually exploded when the lower assembly is moved up to the surface.
In order to overcome this problem, U.S. Pat. No. 6,179,064 describes a device of the aforementioned type, wherein a lower assembly comprising a perforation tool, a detonator and control means is lowered into the bottom of a well for example by means of a cable working line. The lower assembly includes a power battery capable of electrically powering a power module in order to trigger the charge, upon receiving a signal from the surface.
The triggering signal is for example a hydrostatic signal sent into the fluid present in the well around the lower assembly. Alternatively, the signal is a mechanical signal resulting from a predetermined movement of the lower assembly at the bottom of the well.
Once the charge has exploded, the control module sends a confirmation signal to the surface, this signal being transmitted by means of a valve allowing a hydrostatic signal to be generated. Such a device therefore improves the safety of the operators.
However, this device remains complicated to apply, since it requires hydrostatic communication means between the bottom and the surface.
An object of the disclosure is therefore to obtain a device for triggering a pyrotechnic system intended to be lowered into a well, which is very simple to apply, while guaranteeing maximum safety for the operators.